The technical sector of the invention is more particularly the field of installing lines resting on the sea bottom, and in particular including risers having flexible pipes for extracting oil, gas, or other soluble or fusible material or a suspension of mineral material from under the sea via an underwater well head and up to a floating support, in order to develop production fields installed out at sea, off shore. The main and immediate application of the invention lies in the field of producing oil at sea.
The flexible pipes used as production or service lines for conveying liquid or gaseous hydrocarbons present great mechanical strength, in particular against internal pressure, against traction, and against flattening, and they are usually laid by means of winches or traction devices such as “caterpullers” (i.e. tensioners having crawler tracks fitted with shoes that clamp against the line and that move continuously in translation in order to entrain the line therewith), or indeed by combining both winches and caterpullers.
The traction forces applied by such caterpuller devices on a flexible pipe can be considerable when laying at great depth, and the compression forces exerted by the shoes on the line must be high enough to avoid any relative slip between the shoes and the line.
A control umbilical includes one or more hydraulic lines and/or electric cables for transmitting power and/or information.
The lines referred to as “flexible pipes” are well known in the art and they are described in standards documents published by the American Petroleum Institute (API), and more particularly under the references API 17J and API RP 17 B. Such flexible pipes are manufactured and sold in particular by the supplier Coflexip France.
As a general rule, such flexible pipes comprise inner sealing layers of thermoplastic material associated with layers that withstand the pressure inside the line, generally made of steel or of composite materials. Such flexible pipes are constituted more particularly by assembling layers of tubular thermoplastic materials and strong layers of steel or of composite materials made in the form of spiral-wound strips with touching turns inside the thermoplastic pipe in order to withstand internal bursting pressure, and associated with external reinforcement over the thermoplastic tubular layer and likewise in the form of touching spiral-wound strips, but at a pitch that is longer, i.e. with a smaller helical slope angle, in particular lying in the range 15° to 55°.
In the present description, the term “undersea flexible line” is used more generally to designate a cable, an umbilical, or a pipe capable of accepting a large amount of deformation without giving rise to large return forces, and in particular a flexible pipe.
In the prior art, ships for laying flexible lines at sea are fitted with devices for storing and handling said lines as described below with reference to FIG. 4. Most conventionally, a series of winches or drums of horizontal axis have line portions wound thereon and are arranged adjacent to one another in the longitudinal direction of the ship. The various line portions are thus wound on a plurality of winches, each having a horizontal cylinder between two vertical side plates. In that type of prior art embodiment, the horizontal cylinder needs to present stiffness in bending because the weight of the wound line is taken up entirely by the cylinder.
Furthermore, the weight of the line and of the winch including its vertical side plates is transmitted in full to the motor drive for the drum. This results in the winches necessarily presenting a plate size and a windable capacity in terms of line length that are limited, particularly when the diameter of the line is larger.
With flexible lines of large diameter, such conventional storage on winches as shown in FIG. 4 is often not possible since the minimum radius of curvature of such a flexible line is very large, and in particular may be as much as 5 meters (m) or more, thereby requiring drums to be of very large size and therefore unsuitable for handling.
Thus, in practice, the diameter of the end plates does not exceed 5 m to 10 m for a drum weighing 400 (metric) tonnes (t) to 500 t corresponding to portions of line presenting lengths of less than 10 kilometers (km) and in particular lengths of 1 km to 10 km for line diameters of 50 millimeters (mm) to 300 mm, which is why it is necessary, when laying lines of great length and/or of large diameter, to make use of a large number of winches that are thus arranged adjacent to one another. Finally, connecting together the various line portions in order to constitute a complete line providing a bottom-to-surface connection represents handling operations that are relatively difficult and lengthy to perform and that require the laying ship to be out of operation for long periods of time, thus representing large costs.
Devices are also known for storing and handling flexible lines that involve using “winch” type winder devices having a cylinder on which the line is wound that is vertical, with that type of device either being placed on the deck of the ship or else installed inside the ship, generally at the bottom of a hold. Nevertheless, under such circumstances, the fact that the bottom plate of the winch is arranged horizontally over the deck of the ship means that that plate receives the load in full and needs to be supported by a support and rotation device that must present a very high degree of stiffness so as to be capable, on its own, of withstanding compression forces and also bending and/or twisting forces, since the plate constitutes a turntable that needs to be kept properly plane so that the winch can be rotated about its vertical axis in a manner that is stable and accurate; it is also necessary for said winch to be removable after it has been used in order to release the deck of the ship for other operations.
Installing such equipment is difficult, since it requires the use of powerful hoist means given that the structure carrying the turntable together with said turntable presents a weight in the range 250 t to 750 t, or even more under extreme circumstances. Thus, such equipment can be installed or removed only in a sheltered zone, generally in a port, thereby preventing the ship from being used for a period of four to five days, or even several weeks.
WO 2004/068012 describes devices for storing lines by winding them, such a device comprising a circular turntable mounted over a bottom supporting surface situated above the deck of the ship on which the line storage device is installed.
In WO 2004/068012, the line storage device operates by winding in a mixed carousel and rotary basket mode described in FIG. 4B, in which an umbilical 10422 of small diameter is wound in “basket” mode (in the meaning of the definition given in paragraph (e) below concerning a storage device of the invention), the umbilical being wound against a central cylinder of the storage device, while a line 1044 of larger diameter is wound in “carousel” mode (in the meaning of the definition given in paragraph (b) below in the definition of the modular storage device of the present invention) outside posts or other retaining means of the storage device.
Thus, given the fact that the line 10422 is wound in basket mode, the central cylinder is not covered by an end plate of diameter greater than the diameter of the cylinder. On the contrary, the top opening between the central cylinder and the peripheral means 10406 for retaining the line 10422 is empty.
In contrast, a top plate 10408 is added to the tops of the winding support elements 10406 outside which and against which the line 1044 is wound in carousel mode.
In document WO 2004/068012, of necessity, the umbilical or the line wound in basket mode around the central cylinder must accommodate a smaller minimum radius of curvature and must therefore present a smaller diameter.
The embodiment of the mixed storage device described in WO 2004/068012 presents the drawback of requiring a central cylinder of larger diameter when the lines stored in basket mode are of large diameter, thereby making the storage zone situated between said cylinder and the axis of the basket unusable, so the overall storage capacity is thus severely reduced compared with the storage mode of the present invention. In addition, it is more difficult to perform winding in basket mode with lines or umbilicals of small diameter since winding is not performed under tension and requires more accurate control that is therefore more difficult to perform in order to form concentric turns all lying on a common plane, particularly since the diameter of the line and the diameters of the turns are small.
EP 1 118 572 confirms the analysis given above about the difficulty of winding a multi-turn layer in basket mode, the layer comprising a plurality of concentric turns resting on a common plane and being constituted by a line of small diameter, as is required in basket mode.
In WO 2004/068012, EP 1 118 572, and WO 2009/129223 which describe devices for storing lines by winding on board a ship for laying the lines at sea and including a turntable or a bottom plate, said turntable or bottom plate of the device is situated over the deck of the ship.